Cyclosporin is a specific macromolecular (molecular weight 1202.64) cyclic peptide compound consisting of 11 amino acids, which has broad spectrum of useful pharmacological activities, particularly immuno-suppressive activity and anti-inflammatory activity. Therefore, cyclosporin has been used for suppression of inherent immunological responses of the living body, which are caused by tissue and organ transplantation, for example, transplantation of the heart, lung, liver, kidney, pancreas, bone marrow, skin and cornea, and especially the transplantation or foreign tissues and organs. In addition, cyclosporin is useful for the suppression of hematological disorders such as anemia, various autoimmune diseases such as systemic lupus erythematosus, idiopathic malabsorption syndrome, etc., and inflammatory diseases such as arthritis, rheumatoid disorders, etc. Cyclosporin is useful in treatment of protozoal diseases such as malaria, schistosomiasis, etc., and furthermore, recently it is also used in chemotherapy.
Cyclosporin is highly lipophilic and hydrophobic. Therefore, cyclosporin is sparingly soluble in water, and as well dissolved in an organic solvent such as methanol, ethanol, acetone, ether, chloroform and the like. Due to low water-solubility of cyclosporin having above-mentioned properties, when cyclosporin is administered orally, its bioavailability is extremely low and may be greatly influenced by the conditions of each individual patient. Accordingly, it is very difficult to retain an effective therapeutic concentration. Moreover, cyclosporin may show considerable side effects such as nephrotoxicity. Thus, cyclosporin is very difficult to formulate into a preparation for oral administration due to its low water solubility. Accordingly, numerous studies have been extensively conducted to discover a preparation suitable for the effective oral administration of cyclosporin, which can provide a suitable uniform dosage and appropriate bioavailability.
In the prior art, the preparations suitable for oral administration of sparingly water-soluble cyclosporin have been usually formulated in the form of a emulsion pre-concentrate.
One typical method using this combination is taught in U.S. Pat. No. 4,388,307 which issued on Jun. 14, 1983. This patent discloses a liquid formulation of cyclosporin using ethanol. According to the method disclosed in this U.S. Patent Specification, cyclosporin is combined with a carrier consisting of ethanol as a co-surfactant; olive oil as a vegetable oil, and a transesterification product of a natural vegetable oil triglyceride and a polyalkylene polyol as a surfactant to form the liquid formulation. However, the resulting liquid formulation is administered as an aqueous dilution which makes it very difficult to adapt the subject to its administration and to provide a uniform dosage for oral administration.
In order to mitigate the inconvenience of diluting the cyclosporin liquid composition in water prior to oral administration, a liquid composition in the form of an emulsion pre-concentrate has been formulated into a soft capsule preparation, which is now commercially available as Sandimmun.RTM.. In this case the cyclosporin soft capsule contains ethanol due to the solubility requirements of cyclosporin. However, since ethanol may permeate the gelatin shell of the capsule as it is volatile even at normal temperature, to prevent the volatilization of ethanol from the soft capsule preparations during storage and distribution, the soft capsule preparations may be wrapped in a special packing material, such as an aluminium-aluminum blister package.
Recently it has been possible to develop a cyclosporin preparation which has a stability during the storage period and further provides substantially no change in biological availability and its difference between individual subjects, so that the biological effect of cyclosporin can be uniformly maintained. One of the preparations developed for this purpose is disclosed in Korean Laid-open Patent Publication No. 93-113. This preparation is commercialized under the registered trademark Sandimmun Neoral. However, since this preparation also uses ethanol, it may have some disadvantages as in the prior ethanol-containing preparations, in storage stability, and changes in the ethanol content.
Accordingly, the present inventors have studied numerous combinations of various surfactants, oil components, co-surfactants etc., to find a cyclosporin composition which is stable, and provides higher bioavailability and lower difference in blood levels between individual subjects than those of the prior cyclosporin preparations in view of their pharmacokinetic properties. As a result, we have identified that a certain cyclosporin composition consisting of the components as defined below can satisfy the above-mentioned requirements, and then completed the present invention.